Laboratory fume hood



June 7, 1966 A. TRUHAN LABORATORY FUME HOOD 8 Sheets-Sheet 1 Filed May 24, 1965 INVENTOR ANDREW TRUHAN ATTORNEW June 7, 1966 A. TRUHAN LABORATORY FUME HOOD 8 Sheets-Sheet 2 Filed May 24, 1965 INVENTOR ANDREW TRUHAN ATTORNEY! June 7, 1966 A. TRUHAN LABORATORY FUME noon 8 Sheets-Sheet 3 Filed May 24, 19 5 INVENTOR ANDREW TRUHAN 38 BY ,,4 z// ATTORNEXQ June 7, 1966 A. TRUHAN LABORATORY FUME HOOD 8 sheets sheet 4 302 268 L's lirlliluqllliinrl vilwrrniuhxi F lllilllll Ill lllllllllll Filed May 24, 1965 I NVENTOR. ANDREW TRUHAN FIG. 8

A TTORNE Y1 A. TRUHAN LABORATORY FUME HOOD June 7, 1966 8 Sheets-Sheet 5 Filed May 24, 1965 ANDREW TRUHAN Jam/Z Mama F m V 2 m Al m w a m 0 2 2 2 1| M 0 0000000000000 000000000000000000000 H lll l n 00000000000 000000 00000 00000000000 WI 0 0000 0000000000000000000000000000000 0o000 000000000000000000000000000.0000 0 0 a o 0 A TTORNEYJ.

June 7, 1966 A. TRUHAN' 3,254,588

LABORATORY FUME HOOD Filed May 24, 1965 8 Sheets-Sheet 6 FIG. IO

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INVENTOR. FIG. ANDREW TRUHAN A TTORNEYS A. TRUHAN LABORATORY IUME HOOD June 7, 1966 8 Sheets-Sheet '7 Filed May 24, 1965 W ATTORNEY! INVENTOR. ANDREW TRUHAN I II I I A I z June 7, 1966 A. TRUHAN LABORATORY FUME HOOD 8 Sheets-Sheet 8 Filed May 24, 1965 lNVENTOR- -'ANDREW TRUHAN A TTORNE Y5.

United States Patent 3,254,588 LABORATORY FUME HOOD Andrew Truhan, RD. 3, Box 392T, Somerset, NJ. Filed May 24, 1965, Ser. No. 463,456 7 Claims. (Cl. 98-415) This application is a continuation-in-part of my application Serial No.'356,698, filed March 31, 1964, now abandoned, which is a continuation-in-part of my application Serial No. 107,767, filed May 4, 1961.

This invention relates to new and useful improvements in laboratory fume hoods and, in particular, to a fume hood having a balanced air supply and exhaust system and a controlled air flow pattern whereby the hood operates without transference of air from the hood to the laboratory or the laboratory to the hood through the hood access opening.

A further object of the invention is to provide such a hood wherein the air is removed uniformly across the back of the hood thereby eliminating zones of high and low air flow, dead air pockets and the like, thus permitting utilization of the hood for the removal of heavier or lighter than air gases and particulate material.

Another object is to provide a hood provided with a unique perforated partition member extending between the top, bottom and side walls of the hood and spaced from the back wall thereof to define with the back wall.

I mitting the heating and cooling systems for the laboratory to be sized for the room without regard to the number of fume hoods to be installed therein or without regard to their operating periods.

Another object is to provide such a hood wherein the volume of air passing through the hood may be controlled by the operator through means interconnecting variable speed controls on the exhaust and input fans and the air supply inlet openings whereby as the flow of air through the hood is reduced, the air inlet slots are reduced thus increasing the discharge velocity with the quantity of air reduction to maintain a relatively constant air flow pattern to effect a relatively constant air pattern through the hood regardless of the rate of fiow of air.

Another object is to provide such a hood wherein puffing and bucking resulting from converging air flow patterns is maintained at a minimum thereby substantially eliminating interference between the'hood air flow and experiments being conducted within the hood.

These and other objects and advantages are provided by a fume hood comprising top, side, back'and bottom walls, a front frame defining an access opening, and closure means movably mounted in said frame, a rear panel having a plurality of openings generally uniformly. distributed over the area thereof, the rear panel extending between the top, side and bottom walls, and being spaced from the back wall to define therebetween an exhaust plenum chamber, an exhaust fan connected to the exhaust plenum chamber, an air channel formed in each of the side members of the front frame, an air supply fan connected to the air channels, and at least two air outlet passages from each of the channels into the hood, the outlet passages extending vertically substantially from the bottom to the top of the hood, and directing inlet air generally across the access opening, across theside walls, and diagonally across the hood.

Other objects and advantages will be more apparent to those skilled in the art from the following detailed description of the present invention when considered with the illustrative embodiments of a preferred form of the invention wherein:

FIG. 1 is a fragmentary vertical sectional view of a laboratory fume hood constructed in accordance with the present invention;

FIG. 2 is a transverse sectional view substantially on line 2-2 of FIG. 1;

FIG. 3 is a vertical sectional view substantially on line 3-3 of FIG. 1;

FIG. 4 is an enlarged fragmentary sectional view substantially on line 4-4 of FIG. 1 and illustrating in detail one of the air channels formed in the front frame and air outlets therefrom;

FIG. 5 is an enlarged fragmentary sectional view substantially on line 55 of FIG. 1 showing in detail the means for simultaneously controlling the speed of the exhaust' and input fans and the position of the air outlet vanes into the hood;

FIG. 6 is an enlarged fragmentary side view of the hood of the invention showing means for supporting apparatus from the air distribution panel of the hood;

FIG. 7 is a front elevational view, partially in section, illustrating'a modified form of the present invention;

FIG. 8 is a top plan view of the structures shown in FIG. 7;

FIG. 9 is a section on line 99 of FIG. 8;

FIG. 10 is a section on line 1010 of FIG. 9; I

FIG. 11 is a section on line 1111 of FIG. 9;

FIG. 12 is a perspective fragmentary view of the structures illustrated in FIGS. 7 through 11;

FIG. 13 is a fragmentary top plan view of the top portion of a fume hood constructed in accordance with the present invention; and

FIG. 14 is a fragmentary partial sectional view similar to that illustrated in FIG. 12.

Referring to the drawings, 10 generally designates a fume hood constructed in accordance with the teachings of the present invention. The hood 10 includes an outer casing comprising a back panel 14, a bottom panel 16, side panels 18 and 20, and a front panel 22. I

The front panel 22 in cooperation with portions of the respective side panels 18 and 20 is shaped to provide a frame type front access opening generally designated 24 and comprising side frame members 26 and 28, bottom frame member 30 and top frame member 32.

The hood also includes an inner rear wall 34, a top wall 36, a bottom wall 38, and a pair of side walls 40 and 42. As more clearly shown in FIG. 2, the side walls 40 and 42 are spaced inwardly of their respective side members 18 and 20 of the outer casing and the space between-each of these wall members is sectioned oif by a pair of front partition members 44 and 46 and a pair of rear partition members 48 and 50.

The assembly also includes a rear panel generally designated 52 which rear panel has a plurality of openings 54 therethrough generally uniformly distributed over the area thereof. The panel 52 is spaced from the back wall to provide an exhaust plenum chamber 56 between the inner surface of the back wall 34 and the back surface of the panel 52.

In the illustrated form of the invention, the uppermost portion 58 of the back panel 52 slopes generally for wardly to join with the top wall 36 to provide an enlarged zone 60 for the plenum chamber 56. Also, as illustrated in the drawings, the rear panel 52 is provided with side wing portions 62 and 64 which join with the inner side walls 40 and 42, respectively, whereby the plenum chamber 56 extends along the side walls 40 and 42 to the vertically extending pair of partition members 48 and 50. The side panels 62 and 64 of the rear panel 52 are also provided with uniformly distributed openings 54 whereby during operation of the hood of the invention, air is also withdrawn from the hood operating zone in these areas. However, it is to be particularly noted that the rear panel 52 need not be provided with the side extensions 62 and 64 or the sloping top portion 58 whereby the rear panel would extend in a single plane between the top, side and bottom walls and in spaced relationship from the back wall 34.

The top 36 of the hood 10 supports an exhaust duct 68, the lower end 70 thereof communicating with the upper enlarged portion 60 of the exhaust plenum chamber 56 while the opposite end of the conduit 68 discharges the exhaust air and fume removed from the hood at a suitable location. The duct 68 is provided with an exhaust fan 72 driven by a variable speed motor 74 through suitable drive means such as the belt-and-pulleys generally illustrated at 76 in FIG. 3 of the drawings. The motor 74 is provided with power leads 78 which are connected to conventional motor speed control means such as the rheostat 80' illustrated in FIG. of the drawings.

The top 36 also supports one or more lighting fixtures 82 which are also suitably connected to a source of current. 7

Along the front wall 22 and generally supported by the top 36 of the hood is a large inlet plenum chamber 84. The plenum chamber 84 has connected thereto a pair of inlet fans 86 and 88 driven by a common variable speed mot-or 90 which motor is connected by suitable leads 92 to the variable speed control 80. The fans 86 and 88 draw air from a further inlet plenum chamber 94 which is connected to an intake duct 96. The remote end of the intake duct 96 may be connected to a source of air outside of the laboratory whereby the heating and air conditioning system for the laboratory is not unbalanced by operation or discontinuance of operation of the hood. Preferably, the further inlet plenum chamber 94 is provided with a suitable air filter means 98 whereby the supply air for the hood may be supplied in a relatively particulate matter free form. Also, where desired, the air supply system may include air heater means generally indicated at 100 whereby the inlet air may be suitably warmed during cold weather operation or during the summer where it is desired to regulate the temperature of the air passing through the hood.

The plenum chamber 84 supplies air to a pair of air channels 102 and 104 formed in each of the side members of the front frame 24. The air channels are formed from the front panel 22, the side members 18 and 20 of the hood casing; the inner side walls 40 and 42 of the hood, the top 36 and the vertically extending partition members 44 and 46 as more clearly illustrated in FIG.s 2 and 4 of the drawings. These air channels 102 and 104 extend the full height of the hood and each air channel 102 and 104 is provided with a plurality of outlet passages which, in the preferred form of the invention, are variable as to be more fully described hereinafter.

In the illustrated form of the invention, each air channel is provided with three air outlet passages generally designated 106, 108, and 110 for air channel 102 and 106', 108, and 110' for air channel 104. These air outlet passages extend from the bottom 38 to the top 36 of the hood. Where a variable air supply and exhaust system is utilized in the hood, the air outlet passages are also variable to maintain a constant air flow pattern proportioned to the rate of air flow desired through the hood.

The air outlet passages are provided by adjustable baflie structures including an. arcuate panel 112-112' provided with a wedge-shaped base member 114 and a wedge-shaped top portion 115. Each arcuate panel is provided with three radially extending flanges 116, 118 and 120. Flange 116 is positioned adjacent slot 122 while flange 118 is positioned adjacent slot 124. Further, the assembly includes a stationary arcuate plate 126 which is secured at its lower end to the bottom 38 of the hood and at its upper end to the top of the hood 36 by welding or conventional screws or the like. The stationary arcuate plate 126 is provided with a pair of flanges 128 and 130. Flange 128 cooperating with flange 116 and groove 122 generally controls the flow of air issuing from air passage 106 or 106' while flange 130 cooperating with the slot 124 and baflle 118 regulates the flow of air from outlet 108 or 108'. The size of outlet passage 110 or 110' is controlled by the relative position of the flange 120 on the movable panel 112 or 112' c0- operating with the portion of the inner Wall of the respective side members 140 and 142. The bases 114 and the tops 115 of the movable partition members 112 and 112' are mounted for rotation about shafts or pins 134 whereby when the members 112 and 112 are pivoted about the axis of their pins or shafts 134, the outlet air passages 106, 108, 110, and 106', 108', 110' are opened when the speed of the inlet fan motor and the exhaust fan motor 74 is increased and closed when the speed of said motors is decreased to maintain relatively constant the air flow pattern through the hood.

In order to bring about this interrelated movement of the air outlet passages and the speed of the motors, the hood is provided with a conventional motor speed regulating means 80' having a control knob 82 positioned on the front wall 22 of the hood. The motors are connected through the motor speed regulator through conductors 136 which are suitably connected to conductors 78 and 92 of the fan drive motors. A shaft extension 140 of the variable speed control 80 is provided with a bevel gear 142 which is in constant mesh with a bevel gear 144 secured to one end of a shaft 146 which extends across the hood in the zone of the plenum chamber 84. The extended ends of the shaft 146 are suitably received in conventional bearing means 148 and 150. Shaft 146 has secured thereto a pair of bevel gears 152 and 154. Bevel gear 152 is in constant mesh with bevel gear 156 secured to shaft 134 which mounts the movable panel member 112. Bevel gear 154 is in constant mesh with bevel gear 158 which, in turn, is secured to rotate with the shaft from the lefthand side of the air distributing means. With the foregoing structures, as the operator varies the speed of the exhaust and input fan motors through control knob 82', the openings 106, 108, 110 and 106', 108' and 110' are also varied. Thus, with the hood operating at capacity, that is, with maximum hood air quantity, the outlet air passages 106, 108, 110, 106', 108', and 'are at a maximum open position. As the air flow through the hood is reduced by reducing the speed of rotation of the exhaust fan and the inlet fan, the area of the air outlet passages are correspondingly reduced. The reduction in the size of the openings 106, 108, 110, 106', 108', and 110' will increase the discharge velocity of the air proportionately to the reduction in air flow, thereby maintaining a constant air flow pattern through the hood regardless of the quantity of air being handled.

Referring particularly to FIG. 2, the air flow pattern across and through the hood is diagrammatically illustrated. In the illustrated pattern, three air outlet passages are provided from each of the air channels 102 and 104. The air outlet passages 106 and 106' generally direct the air across the access opening; air outlet passages 108 and 108 generally direct the air diagonally across the hood toward the rear panel 52 while air outlet passages 110 and 110' generally direct the air parallel with their side Walls 40 and 42 to provide an air flow pattern substantially as shown by the directional arrows. It will be appreciated that while three air outlet passages have been shown for each air channel 102 and 104, a lesser or a greater number of outlet passages may be provided and still maintain substantially the same general air flow pattern.

Also referring to FIG. 2, there are shown reference pressures across the hood with the coordinated exhaust and inlet fan system in operation. The line A-B drawn through the center of the hood from front to rear indicates the zone where the terminal velocity of the air streams without the exhaust fan in operation would be zero so that the air streams from opposite air channels 192 and 104 would meet without substantial velocity along this line. Since the capacity of the inlet and exhaust fan systems is sized to provide for balanced operation, with the exhaust fan in operation there is a positive velocity toward the rear of the hood which increases as the rear of the hood is approached as indicated by the numerals 0, 1, 1 /2 and 2. Thus, the action of the exhaust fan bends the supply air stream toward the rear and cooperates to substantially eliminate turbulence caused by converging air streams from the opposite air inlet channels.

As hereinbefore set forth, the hood of the invention is designed so that it may be effectively operated without a front wall; however, as illustrated in the drawings, a window 160 provided with a sash 162 is slidably received in channel elements 164 and 166 provided in the frame 24 at the front of the hood. The window 160 slides upwardly in front of the plenum chamber 84 for the air supply. In FIG. 3, the window 160 is shown in full lines in the closed position and in phantom lines in the open position. Normally, the hood is to be operated with the window 160 closed so that uncontrolled movements of air externally of the hood do not affect the uniform flow pattern of the air within the hood and it is particularly pointed out that during such normal operation of the hood, the window 160 is completely closed to insure that there is no transfer of room air to the hood or air and gases from the hood to the room through the front access opening.

The single section through the hood shown in FIG. 3 is typical of the air flow through any horizontal section as the static pressure drop across the perforated backboard 52 sets up a negative pressure in the exhaust air plenum chamber, thereby effecting a relatively equal amount of air flow through each of the plurality of uniformly distributed openings 54 in the backboard and its side extensions 62 and 64. Regarding the openings in the side panels 62 and 64, it will be noted from FIG. 2 that the space between the perforated panel 52 and the back Wall 34 is greater than that adjacent the side panels 62 and 64 whereby the air flow through these portions of the sides are controlled so that a negative pressure will be effective in relation to the hood operating space but not as negative as the exhaust air in the larger portion of the plenum chamber rearwardly of the perforated panel 52. Therefore, the air flow through each of the openings in the rear 7 panel 52 will be greater than the air flow through each of 1 port elements such as illustrated at 180 in FIG. 6 wherein a conventional flask 182 is illustrated as being supported within the hood from the releasable support hangers received in certain of the openings in the perforated panel 52. It will be appreciated that depending on the accessories desired to be placed within the hood, various shapes and arrangements of clamping devices and supports for condensers, beakers, thermometers, and the like 7 will be utilized in conjunction with the uniform air distributing perforated rear panel 52.

From the foregoing description of the hood of the invention and the reference drawings, it will be seen that the present invention fully accomplishes the aims and objects herebefore set forth. It will be appreciated by those skilled in the art that various modifications may be made in the form and arrangement of the hood without departing from the inventive contribution defined in the appended claims. Further, it will be appreciated that the hood may be constructed of many types of materials and it is contemplated that the supply air plenum chamber and the front of the hood may be cast as a single unit from a suitable plastic which is resistant to the corrosive effects of chemicals to be employed in the hood.

It will also be appreciated that the space between the outer walls 46 and 42 and the inner walls 18 and 20 defined by the two pairs of vertically extending partitions 44 and 46 and 48 and 50 may be utilized in supplying the hood with electrical power, water, gas and the like with valve operators for the equipment being provided along the front panels 22 so that complete operation of the hood, electrical, gas, water and fume removal system may be at the control of an operator observing the experimental equipment from the front of the hood.

Referring particularly to FIGS. 7 through 14, a modified form of the present invention is illustrated. In the description of FIGS. 7 through 14, elements of this form of the invention corresponding to those illustrated in FIGS. 1 through 6 are generally given like reference characters preceded by the numeral 2.

The fume hood 210 includes an outer casing comprising a back panel 214, a bottom panel 216, side panels 218 and 220, and a front panel 222. The front panel 222, like the front panel 22 of the prior form of the invention, includes frame members 226 and 228 which slidably receive a hood closure window 260.

The closure window 260 is provided with a pair .of counter-balance weights 265 and 265, which weights are connected to the upper edge of the window 260 by flexible draft members 267 and 267'. Each flexiblev draft member 267 and 267' is turned over a pulley 268 and 268 respectively. Details of the pulley and weight conthe hood itself.

As in the prior form of the invention, the hood includes an inner back wall 252 provided with perforations 254 uniformly distributed over its entire surface; .The inner wall 252 is spaced inwardly of the outer wall 214 to provide an outlet plenum chamber 256, between the inner surface of the outer wall 214 and the outer surface of the inner wall 252. The hood is also provided with side walls 240 which, like the prior form of the invention, are spaced inwardly of the outer walls 218 and 220.

The more rearward portions of the inner side walls 240 comprises perforated sections 262. The perforations 264 in sections 262 may be sized and positioned similar to the sizing and positioning of the perforations 254 in the inner back panel 252.

The space between the inner side panels 240 and the I correspondingouter walls provide air flow passages 270 which communicate at their upper ends with the air flow control fan means 272. Specifically, the output from the air control fan 272 passes into a tapered channel 274, after passing through a set of air flow control and divider vane means 276. The flow control and divider vanes 276 directhalf of the air flow into channel section 278 and half in-to channel section 280. From the reduced area ends of the flow control channel member 274 the air respectively passes through turning vanes 282 at each end of the hood which turning vanes cause the air flow to pass downwardly into spaces 270.

Wall members 284, sloping from the upper ends of the passages 270 to their lower ends, insure a relatively uniform flow of air through the passages 27%, through perforated panels 286 thence through flow straightening vane elements 288, thence into a plurality of turning vane sets 290 positioned along each of the front panels 226 and 228 of the hood.

The turning vanes 290 are so shaped that the vanes have a uniform spacing at the inlet ends, designated 292, and at the outlet ends 294. In passing from the inlet ends 292 to the outlet ends 294 of the vane sets 290, different portions of the air stream are provided with different directions of flow. For example, referring to FIG. 11, arrow A illustrates the direction of a portion of the inlet air stream which is generally parallel across the access opening of the hood to provide an air curtain or wall therefor, arrow B illustrates the portion of air stream directed generally diagonally across the fume hood, while arrow C illustrates the portion of the air stream intermediate a line passing diagonally through the hood and its respective side Walls. Thus turning vanes 282, perforate panel 286, straightening vanes 28% and turning vanes 290 produce an air flow pattern across and through the hood of the type illustrated-in FIG. 2 of the drawings and accomplish the uniform distribution of the inlet air as discussed hereinbefore.

The novel means hereinabove discussed in cooperation with the perforate back panel 252 and the perforate side sections 262 forming part of each'of the side panels cooperate to maintain the uniform air distribution throughout substantially all vertical cross sections of the hood. At the same time, as in the prior form of the invention, the uniform air movement through the hood is of a substantial volume but at a low velocity, whereby if, for example, a Bunsen burner is to be operated within the hood, the air flow would not create difficulties in maintaining the burner flame.

The air flowing through the hood as illustrated, for example, in FIGS. 9 and 11 pass through the perforate panel 252 and 262 into the outlet plenum chamber 256 thence into duct 298. From duct 298 all of the air stream may be discharged through suitable ducts to disposal outside of the building, or where desired, all or a portion thereof may be recirculated through the hood.

In order to provide the necessary control for the hood of the present nature, a separate exhaust fan meansSttO is provided for connection to the outlet duct 298 which fan is illustrated in FIG. 13 of the drawings. Where none of the air having passed through the hood is to be recirculated, the fan 272 draws in fresh air through inlet 302 and inlet 302 may be provided with one or more air filter means generally designated 394.

Further, as illustrated in FIGS. 7 and 13, the inlet air may pass through electrical heater means 306 prior to passage of the air through the fan means 272 and thence into the hood. The heater means would be of substantial importance Where all of the air to be provided for the hood is drawn from the ambient atmosphere and a relative uniform temperature above ambient is to be maintained within the hood.

Again referring to FIG. 13, auxiliary means 398 and 310 may be mounted in the upper portion of the hood adjacent the intake to the fan or blower 272 and have connection to the inlet air duct. The auxiliary means 308 may comprise a source of carbon dioxide which may be manually or automatically directed into the air stream in the event of fire Within the hood. The other chamber 310 may contain a supply of ethylene glycol as an air sterilizing means. -It will be appreciated that other sterilizing and fire extinguishing and the like means may be connected to the inlet chamber for the hood without departing from the scope of the present invention. Further, while not specifically illustrated, each of the fans 272 and 300 is connected to separate speed control means 3% whereby the operator may control the rate of flow of air through the hood. However, where desired, the two controls may be interlocked such that regardless of the rate of flow in and out, the in-and-out flow is substantially equal, so that with the window 260 open air neither enters nor leaves through the opening.

It has also been found desirable to provide warning lights in conjunction with the control means for the fans, particularly where the controls are separate, whereby the operator is immediately signaled by the lights in the event the output fan and the input fan are not adjusted for a uniform flow of air through the hood.

From the foregoing description of the various forms of the present invention it will be seen that the objects and advantages hereinbefore set forth are fully accomplished.

I claim:

1. A fume hood comprising top, side, back and bottom walls, a front frame defining an access opening, and closure means movably mounted in said frame, a rear panel having a plurality of openings generally uniformly distributed over the area thereof, said panel generally extending between the top, side and bottom walls and being spaced from the back wall to define therebetween an exhaust plenum chamber, an exhaust fan connected to the exhaust plenum chamber, an air channel formed in each of the side members of the front frame, an air supply fan connected to said air channels, a plurality of outlet passages from each of said channels into said hood, said outlet passages extending vertically substantially from the bottom to the top of the hood and directing inlet air generally across the access opening, across the side walls and diagonally across the hood.

2. A fume hood comprising top, side, back and'bottom walls, a front frame defining an access opening, and closure means movably mounted in said frame, a rear panel having a plurality of openings generally uniformly distributed over the area thereof, said panel generally extending between the top, side and bottom walls and being spaced from the back wall to define therebetween an exhaust plenum chamber, an exhaust fan connected to the exhaust plenum chamber, an air channel formed in each of the side members of the front frame, an air supply fan connected to said air channels, at least three outlet passages for each of said channels into said hood, each of said outlet pasages extending vertically substantially from the bottom to the top of the hood and directing inlet air generally across the access opening, across the side walls, and diagonally across the hood.

3. A fume hood comprising top, side, back and bottom walls, a front frame defining an access opening, and closure means movably mounted in said frame, a rear panel having a plurality of openings generally uniformly distributed over the area thereof, said rear panel extending between the top side and bottom walls and being spaced from the back walls to define therebetween an exhaust plenum chamber, a variable speed exhaust fan connected to the exhaust plenum chamber, an air channel formed in each of the side members of the front frame, a variable speed air supply fan connected to said air channels, motor speed control means for simultaneously varying the speed of the exhaust and air supply fans, at least three outlet passages from each of said air channels for directing air from said channels into said hood, said outlet passages extending vertically substantially from the bottom to the top of the hood and directing inlet air generally across the access opening, across the side walls and diagonally across the hood.

4. The invention defined in claim 3 including means for varying the area of said air outlet passages and means connecting the motor speed control means for the exhaust fan and the air supply fan to said means for varying the outlet area of said air outlet passages.

5. A fume hood comprising top, side, back and bottom walls, a front frame defining an access opening, and closure means movably mounted in said frame, a rear panel having a plurality of openings geenrally uniformly distributed over the area thereof, said panel extending between the top, side and bottom walls and being spaced from the back wall to define therebetween an exhaust plenum chamber, a variable speed exhaust fan connected to the exhaust plenum chamber, an air channel formed in each of the side members of the front frame, a variable speed air supply fan connected to said air channels, and a plurality of air outlet passages for each of said channels for directing air into said hood, said outlet passages extending vertically substantially from the bottom to the top of the hood and directing inlet air generally across the access opening, across the side walls, and diagonally across the hood and equipment support hangers removably receivable in certain of the openings in the said rear panel for supporting equipment within the hood.

6. The invention defined in claim 5 including a plurality of openings generally uniformly distributed over the area of a portion of each of the side Walls immediately adjacent to said rear panel and having communication with the exhaust plenum chamber, and equipment support hangers removably receivable in selected openings in said side panels.

7. A method of operating a laboratory fume hood comprising directing a pair of streams of air into a fume hood along opposite generally parallel paths contiguous with an openable access door, causing each of the pair of air streams to flow in a generally diagonal opposed direction from the front to the rear of the fume hood, and exhausting gas from the hood over an area co-extensive with the back of the hood and a portion of the side and top walls, the rate of exhaustion of the gas and the rate of air input into the hood being balanced whereby flow of ambient air into the hood or gas from the hood through the access door is reduced to substantially zero flow.

No references cited. 

1. A FUME HOOD COMPRISING TOP, SIDE, BACK AND BOTTOM WALLS, A FRONT FRAME DEFINING AN ACCESS OPENING, AND CLOSURE MEANS MOUNTED IN SAID FRAME, A REAR PANEL HAVING A PLURALITY OF OPENINGS GENERALLY UNIFORMLY DISTRIBUTED OVER THE AREA THEREOF, SAID PANEL GENERALLY EXTENDING BETWEEN THE TOP, SIDE AND BOTTOM WALLS AND BEING SPACED FROM THE BACK WALL TO DEFINE THEREBETWEEN AN EXHAUST PLENUM CHAMBER, AN AIR CHANNEL FORMED IN EACH EXHAUST PLENUM CHAMBER, AN AIR CHANNEL FORMED IN EACH OF THE SIDE MEMBERS OF THE FRONT FRAME, AN AIR SUPPLY FAN CONNECTED TO SAID AIR CHANNELS, A PLURALITY OF OUTLET PASSAGES FROM EACH OF SAID CHANNELS INTO SAID HOOD, SAID OUTLET PASSAGES EXTENDING VERTICAL SUBSTANTIALLY FROM THE BOTTOM TO THE TOP OF THE HOOD AND DIRECTING INLET AIR GENERALLY ACROSS THE ACCESS OPENING, ACROSS THE SIDE WALLS AND DIAGONALLY ACROSS THE HOOD. 